delphi - 如何修改 TComponentProperty 以仅显示下拉列表中的特定项目？

Question

请考虑这样的场景:

我有一个名为 TMenuItemSelector 的组件，它有两个已发布的属性: PopupMenu - 允许从表单中选择 TPopupMenu 的实例， >MenuItem 允许从表单中选取TMenuItem 的任何实例。

我想修改 MenuItem 属性的属性编辑器，以便在分配 PopupMenu 时，仅显示此 PopupMenu 中的菜单项在下拉列表中可见。

我知道我需要编写自己的 TComponentProperty 后代并重写 GetValues 方法。问题是我不知道如何访问 TMenuItemSelector 所在的表单。

原始TComponentProperty正在使用此方法来迭代所有可用实例:

procedure TComponentProperty.GetValues(Proc: TGetStrProc);
begin
  Designer.GetComponentNames(GetTypeData(GetPropType), Proc);
end;

但是，Designer 似乎是预编译的，因此我不知道 GetComponentNames 是如何工作的。

这就是我到目前为止所拥有的，我想我唯一缺少的是 GetValues 的实现:

unit uMenuItemSelector;

interface

uses
  Classes, Menus, DesignIntf, DesignEditors;

type
  TMenuItemSelector = class(TComponent)
  private
    FPopupMenu: TPopUpMenu;
    FMenuItem: TMenuItem;
    procedure SetPopupMenu(const Value: TPopUpMenu);
    procedure SetMenuItem(const Value: TMenuItem);
  published
    property PopupMenu: TPopUpMenu read FPopupMenu write SetPopupMenu;
    property MenuItem: TMenuItem read FMenuItem write SetMenuItem;
  end;

type
  TMenuItemProp = class(TComponentProperty)
  public
    function GetAttributes: TPropertyAttributes; override;
    procedure GetValues(Proc: TGetStrProc); override;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterPropertyEditor(TypeInfo(TMenuItem), TMenuItemSelector, 'MenuItem', TMenuItemProp);
  RegisterComponents('Test', [TMenuItemSelector]);
end;

{ TMenuItemSelector }

procedure TMenuItemSelector.SetMenuItem(const Value: TMenuItem);
begin
  FMenuItem := Value;
end;

procedure TMenuItemSelector.SetPopupMenu(const Value: TPopUpMenu);
begin
  FPopupMenu := Value;
end;

{ TMenuItemProperty }

function TMenuItemProp.GetAttributes: TPropertyAttributes;
begin
  Result := inherited GetAttributes + [paValueList, paSortList];
end;

procedure TMenuItemProp.GetValues(Proc: TGetStrProc);
begin
  //How to filter MenuItems from the form in a way that only
  //MenuItems which belong to TMenuItemSelector.PopupMenu are displayed? \
  //And how to get to that form?
  //inherited;

end;

end.

有人可以帮忙吗？

谢谢。

Answer 1

当调用TMenuItemProp.GetValues()时，您需要查看当前正在编辑其MenuItem属性的TMenuItemSelector对象，请参见如果该对象分配了 PopupMenu，如果是这样，则按需要循环遍历其项目，例如:

procedure TMenuItemProp.GetValues(Proc: TGetStrProc); 
var
  Selector: TMenuItemSelector;
  I: Integer;
begin 
  Selector := GetComponent(0) as TMenuItemSelector;
  if Selector.PopupMenu <> nil then
  begin
    with Selector.PopupMenu.Items do
    begin
      for I := 0 to Count-1 do
        Proc(Designer.GetComponentName(Items[I]));
    end;
  end else
    inherited GetValues(Proc);
end; 

顺便说一句，您需要在单独的包中实现TMenuItemSelector和TMenuItemProp。除了 RegisterComponents() 函数(在运行时包中实现)之外，不允许将设计时代码编译为运行时可执行文件。它违反了 EULA，并且不允许分发 Embarcadero 的设计时包。您需要在仅运行时包中实现 TMenuItemSelector，然后在仅设计时包中实现 TMenuItemProp 和 Register()， >需要仅运行时包并使用声明TMenuItemSelector的单元，例如:

unit uMenuItemSelector;

interface

uses
  Classes, Menus;

type
  TMenuItemSelector = class(TComponent)
  private
    FPopupMenu: TPopUpMenu;
    FMenuItem: TMenuItem;
    procedure SetPopupMenu(const Value: TPopUpMenu);
    procedure SetMenuItem(const Value: TMenuItem);
  protected
    procedure Notification(AComponent: TComponent; Operation: TOperation); override;
  published
    property PopupMenu: TPopUpMenu read FPopupMenu write SetPopupMenu;
    property MenuItem: TMenuItem read FMenuItem write SetMenuItem;
  end;

implementation

{ TMenuItemSelector }

procedure TMenuItemSelector.Notification(AComponent: TComponent; Operation: TOperation);
begin
  inherited;
  if Operation = opRemove then
  begin
    if AComponent = FPopupMenu then
    begin
      FPopupMenu := nil;
      FMenuItem := nil;
    end
    else if AComponent = FMenuItem then
    begin
      FMenuItem := nil;
    end;
  end;
end;

procedure TMenuItemSelector.SetMenuItem(const Value: TMenuItem);
begin
  if FMenuItem <> Value then
  begin
    if FMenuItem <> nil then FMenuItem.RemoveFreeNotification(Self);
    FMenuItem := Value;
    if FMenuItem <> nil then FMenuItem.FreeNotification(Self);
  end;
end;

procedure TMenuItemSelector.SetPopupMenu(const Value: TPopUpMenu);
begin
  if FPopupMenu <> Value then
  begin
    if FPopupMenu <> nil then FPopupMenu.RemoveFreeNotification(Self);
    FPopupMenu := Value;
    if FPopupMenu <> nil then FPopupMenu.FreeNotification(Self);
    SetMenuItem(nil);
  end;
end;

end.

.

unit uMenuItemSelectorEditor;

interface

uses
  Classes, DesignIntf, DesignEditors;

type
  TMenuItemSelectorMenuItemProp = class(TComponentProperty)
  public
    function GetAttributes: TPropertyAttributes; override;
    procedure GetValues(Proc: TGetStrProc); override;
  end;       

procedure Register;

implementation

uses
  Menus, uMenuItemSelector;

procedure Register;
begin
  RegisterComponents('Test', [TMenuItemSelector]);
  RegisterPropertyEditor(TypeInfo(TMenuItem), TMenuItemSelector, 'MenuItem', TMenuItemSelectorMenuItemProp);
end;

{ TMenuItemSelectorMenuItemProp }

function TMenuItemSelectorMenuItemProp.GetAttributes: TPropertyAttributes;
begin
  Result := inherited GetAttributes + [paValueList, paSortList] - [paMultiSelect];
end;

procedure TMenuItemSelectorMenuItemProp.GetValues(Proc: TGetStrProc);
var
  Selector: TMenuItemSelector;
  I: Integer;
begin
  Selector := GetComponent(0) as TMenuItemSelector;
  if Selector.PopupMenu <> nil then
  begin
    with Selector.PopupMenu.Items do
    begin
      for I := 0 to Count-1 do
        Proc(Designer.GetComponentName(Items[I]));
    end;
  end else
    inherited GetValues(Proc);
end; 

end.